August 17, 2004
From: ProMED-mail<promed@promedmail.org>
Source: British Soc Plant Pathol, New Disease Reports Vol. 9 [edited]

Occurrence of pith necrosis caused by _Pseudomonas fluorescens_ on tomato plants in Turkey

H Saygili <saygili@ziraat.ege.edu.tr>, Department of Plant Protection, Faculty of Agriculture, Ege University, 35100 Bornova, Izmir, Turkey; Y Aysan, M Mirik, Department of Plant Protection, Faculty of Agriculture, Cukurova University, 01330 Balcali, Adana, Turkey; F Sahin, Department of Plant Protection, Faculty of Agriculture, Ataturk University, 25240 Erzurum, Turkey. Accepted for publication: 5 Jul 2004.

Pith necrosis, caused by _Pseudomonas corrugata_, _P. viridiflava_, _P. fluorescens_ and _P. mediterranea_, is one of the most destructive diseases of tomato in Europe. The disease of soil-grown greenhouse tomatoes was observed in Adana, Mersin, Antalya, Mugla and Izmir, in the Mediterranean and Aegean regions of Turkey, during late winter and spring of 2002 and 2003.

Symptoms were yellowing and wilting of lower leaves which progressed upwards, brown areas on stems and yellow-brown discoloration of the pith.
Bacteria were consistently isolated from affected plants and these formed fluorescent colonies on King's medium B. 27 bacterial isolates were purified and used for further studies. In tests performed according to Lelliott & Stead (1987), all isolates were Gram negative, oxidase, arginine dihydrolase and gelatin liquefaction positive. None caused soft rot on potato slices within 48 h at 25 deg C or produced levan-type colonies on sucrose nutrient agar and all were negative in tobacco hypersensitivity and nitrate reduction tests.

Fatty acid (FA) analysis identified the isolates as _P. fluorescens_ [Pf] biotype I with similarity indices of 55 to 97 per cent (Janse et al, 1992).
Isolates were divided into 2 main clusters on the basis of the FA analysis.

Pathogenicity was tested on 4 week old tomato plants (cv. H-2274) by injecting a 100 million cfu per ml suspension of bacteria into the pith, using a hypodermic syringae. A reference strain of Pf biotype I (CFBP 2101,
France) and saline were used as positive and negative controls respectively. Inoculated plants and saline-inoculated controls were covered with polythene bags for 24 h and maintained in a controlled environment room at 25 deg C, 70 percent relative humidity, with a 16 h photoperiod.

Pith necrosis symptoms developed on inoculated plants in 7 days. No symptoms developed on negative control plants. The bacteria were re-isolated from the inoculated plants and characterised as identical to the reference strain. No differences in the pathogenicity of the isolates were observed. Pith necrosis of tomatoes caused by _Pseudomonas corrugata_ has been reported previously in Turkey (Demir, 1990) but this is the lst report of Pf biotype I causing the disease in Turkey.

References
Demir G. The occurrence of Pseudomonas corrugata on tomatoes in Turkey.
Journal of Turkish Phytopathology 1990; 19: 63-70.
Janse JD, Derks JHJ, Spit BE, van der Tuin WR. Classification of fluorescent soft rot Pseudomonas bacteria, including P. marginalis strains, using whole cell fatty acid analysis. Systematic and Applied Microbiology 1992; 15: 538-53.
Lelliott RA, Stead DE. Methods for the Diagnosis of Bacterial Diseases of Plants. Oxford, UK: Blackwell, 1987.

[Pf is one of several _Pseudomonas_ spp. that cause pith necrosis. Of interest to plant pathologists is that strains of Pf suppress plant diseases by protecting seeds and roots from fungal infection This occurs as a result of the production of several secondary metabolites including antibiotics, siderophores and hydrogen cyanide. Competitive exclusion of pathogens as the result of rapid colonization of the rhizosphere by Pf may also be an important factor in disease control.

Additional references:
<http://www.aces.edu/pubs/docs/A/ANR-0864/ANR-0864.pdf>
<http://www.blackwell-synergy.com/servlet/useragent>
<http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2672.1997.00268.x/abs/> 
<http://genome.jgi-psf.org/draft_microbes/psefl/psefl.home.html>
- Mod.DH]